An electrophoretic display is a device based on the electrophoresis phenomenon of charged pigment particles dispersed in a solvent. The display usually comprises two electrode plates placed opposite of each other and a display medium comprising charged pigment particles dispersed in a solvent is sandwiched between the two electrode plates. When a voltage difference is imposed between the two electrode plates, the charged pigment particles may migrate to one side or the other, depending on the polarity of the voltage difference, to cause either the color of the pigment particles or the color of the solvent to be seen from the viewing side of the display.
Factors which may negatively affect the performance of an electrophoretic display include optical response speed decay of the display and the grey level shift under operating conditions. The decay in performance is often due to photo-exposure, temperature variation and aging of the materials used in the display device.